1. Field of the Invention
The present invention relates to a refrigerant compressor for an air-conditioning system and, more particularly, relates to a single-headed piston type variable capacity refrigerant compressor including a non-clutch type variable capacity refrigerant compressor.
2. Description of the Related Art
A conventional variable capacity refrigerant compressor such as a variable inclination swash plate type refrigerant compressor or a wobble plate type refrigerant compressor is used for compressing a refrigerant gas to be supplied to an air-conditioning system or a climate control system. In the conventional variable capacity refrigerant compressor, a variable inclination swash plate or wobble plate acting as a cam plate to convert a rotating motion of a drive shaft into a reciprocating motion of single-headed pistons within axial cylinder bores is incorporated in a crank chamber, and the cam plate is mounted around the drive shaft in such a manner that its angle of inclination about a fulcrum can be changed with respect to a plane perpendicular to the axis of rotation of the drive shaft. The angle of inclination of the cam plate is adjustably changed by controlling a pressure differential between a first pressure prevailing in the crank chamber and acting on the back end of each of the respective single-headed pistons and a second pressure, i.e., a pressure of the refrigerant gas (a suction pressure) acting on the front end of each of the respective pistons. When the angle of inclination of the cam plate about the fulcrum is adjustably changed, the respective pistons change their reciprocating stroke within the cylinder bores, and accordingly, the amount of the refrigerant gas compressed within the cylinder bores and discharged from the cylinder bores into the discharge chamber of the compressor is varied per one complete rotation of the drive shaft. The controlling of the above-mentioned pressure differential is usually conducted, in response to a change in a refrigerating load applied by the air-conditioning system onto the compressor, by adjustably controlling the first pressure prevailing in the crank chamber via a supply of an adjusted partial amount of the compressed refrigerant gas from the discharge chamber into the crank chamber. The amount of the supply of the compressed refrigerant gas is controlled by a control valve.
Alternatively, the controlling of the above-mentioned pressure differential can be conducted by constantly regulating the first pressure prevailing in the crank chamber, to a predetermined unchanging pressure level, so that a change in the suction pressure due to a change in the refrigerating load directly causes a change in the pressure differential. The regulation of the first pressure is conducted by supplying a partial adjusted amount of the compressed refrigerant gas from the discharge chamber into the crank chamber through a choke provided in a gas passageway extending from the discharge chamber to the crank chamber and by controlling an amount of withdrawal of the gas from the crank chamber toward an appropriate suction pressure region in the compressor via a control valve.
Japanese Unexamined Utility Model Application (Kokai) No. 3-37378 (hereinafter referred to as JP-A-3-37378) discloses a refrigerant compressor for a vehicle climate control system which does not employ a solenoid clutch between an external drive source and a drive shaft of the compressor for connecting and disconnecting a transmission of a drive power from the drive source to the drive shaft. Elimination of the solenoid clutch from the refrigerant compressor for a vehicle climate control system is advantageous from the viewpoint of improving the driving performance of the vehicle engine and of reducing the manufacturing cost and the net weight of the refrigerant compressor.
Nevertheless, a refrigerant compressor with no solenoid clutch as disclosed in JP-A-3-37378 must suffer from a problem such that since the compressor continues to discharge a small amount of the compressed refrigerant gas even when the refrigeration of the vehicle by the climate control system is not necessary, frost is deposited on an outer surface of an evaporator of the vehicle climate control system. Therefore, in the refrigerant compressor of JP-A-3-37378, a particular solenoid-operated valve is arranged in the refrigerant gas conduit running through the climate control system and the refrigerant compressor in order to prevent a return of the refrigerant gas from the system to the suction chamber of the refrigerant compressor. Namely, by preventing the return of the refrigerant gas from the system to the compressor, the discharge of the refrigerant gas from the compressor to the climate control system can be suppressed.
However, in the variable capacity refrigerant compressor with or without a solenoid clutch, while the refrigerant compressor operates under an intermediate capacity condition due to the capacity control made in response to a change in a refrigerating load from the vehicle refrigerating system, the crank chamber receiving a variable inclination type cam plate therein is supplied with a given amount of the compressed refrigerant gas from the discharge chamber via a gas supply passage, and various movable elements such as the cam plate and shoes are lubricated by oil particles suspended in the supplied refrigerant gas. The gas supply passage arranged to extend through a portion of the cylinder block is formed as a straight path extending linearly and having a bore diameter determined so as contribute only to the control of the discharge capacity of the compressor. Thus, as soon as the refrigerant gas suspending therein the lubricating oil particles enters the crank chamber having a large volume, after passing through the gas supply passage, the suspended oil particles are separated from the refrigerant gas due to loss of the flow speed of the refrigerant gas within the crank chamber. Since the interior of the crank chamber is usually maintained at a rather high temperature because of an existence of various moving elements which frictionally generate heat during the operation thereof, the lubricating oil becomes an oil mist within the crank chamber while the oil is agitated by the cam plate rotating or wobbling within the crank chamber. Thus, the oil mist is easily carried by the refrigerant gas toward the suction chamber through a gas withdrawal passage to result in a shortage of the lubricating oil within the interior (a bottom portion) of the crank chamber. Therefore, lack of lubrication for all the movable elements in the compressor occurs.
On the other hand, in the described variable capacity refrigerant compressor without a solenoid clutch, when the solenoid valve is closed to stop the refrigerating operation of the climate control system during the continuous operation of the compressor, the suction pressure within the suction chamber of the compressor responsively falls while causing an operation of the capacity control valve to move the refrigerant compressor to its minimum capacity operation. Accordingly, only a small amount of the refrigerant gas is circulated through the cylinder bores, the discharge chamber, the gas supply passage, the crank chamber, the gas withdrawal passage, and the suction chamber within the compressor. However, the above circulating flow of the refrigerating gas is different from an ordinary circulating flow of the refrigerant gas through the climate control system, and accordingly, the refrigerant gas becomes a high temperature gas which allows the movable elements including the cam plate, the shoes, and the shaft sealing device to be heated by friction during the movements of these movable elements. Consequently, each of the movable elements lacks lubrication, and therefore, the mechanical durability of the movable elements of the refrigerant compressor is reduced to reduce the life of operation of the refrigerant compressor per se.